In a known tire manufacturing method, the tread of a tire and a base tire which provides the base for the tire are fabricated separately. Then an uncured cushion gum is applied to the peripheral surface of the base tire before the tread is applied to the top surface of the cushion gum. And finally the cushion gum is cured, thereby bonding the tread and the base tire together with the cushion gum in between them.
An application surface of a base tire to which a new tread is applied is formed, for instance, by removing the worn tread portion of a used tire with a buffing machine. The base tire formed with the application surface is then subjected to a measurement of the thickness from the steel belt of the base tire to the application surface (hereinafter referred to as “gauge thickness”) along its circumference, and the thinnest thickness is detected from the measurement results as the position of the lightweight point of the base tire. The cushion gum which is wound around the application surface is extrusion-molded by an extrusion molding machine into a predetermined length, which is the circumferential length of a single tire, and a predetermined width. The cushion gum thus extrusion-molded is conveyed by a conveyance means, such as a conveyor, to the position of application to the base tire, and the cushion gum is wound circumferentially with its lead edge at the position of the lightweight point. That is, as the cushion gum is wound around the application surface of the base tire with its joint aligned with the position of the lightweight point, the total of the gauge thickness of the base tire and the thickness of the cushion gum will be approximately even. Thus, when the tread is applied on the cushion gum, a tire superior in uniformity is manufactured.
However, the lead edge of the cushion gum extruded from the extrusion molding machine tends to be thinner than the other part midway through the winding around the application surface because of the smaller amount of extrusion due to the lower temperature of the cushion gum. Also, at the end of winding, where the amount of extrusion is controlled to become small, the tail edge of the cushion gum tends to be thinner than the part midway through the winding. In other words, the alignment of the joint of the cushion gum with the lightweight point of the base tire where the gauge thickness is the thinnest can produce the thinnest point of the base tire around which the cushion gum is wound, thus impairing the uniformity of the tire.